Re: Continuing Problems with 7704A Display



Yes, there's an ~24kHz ripple on those collectors. I'll have to set up the HV test configuration and check whether the snaky traces reappear.

Barry - N4BUQ

----- Original Message -----
From: "Albert Otten" <>
To: "tekscopes" <>
Sent: Sunday, October 17, 2021 2:18:06 PM
Subject: Re: [TekScopes] Continuing Problems with 7704A Display
On Sun, Oct 17, 2021 at 08:14 PM, n4buq wrote:

I had been meaning to check that and, so I just did and, oddly, that has
disappeared. I have nothing but clean, sharp traces now. Weird as I don't
know what I would've done to rectify that. If a low cathode voltage was the
blame, then okay but that seems like an odd cause. Hopefully it doesn't
suddenly return.
My idea is that this is the effect of the 741 being in regulation now. The
feedback can reduce HV drift but also 20 kHz ripple in HV. Check the
Q4105/Q4115 collectors for 20 kHz ripple, it's a good sign when it's present
Make HV somewhat more negative until regulation just stops (collectors near 0 V)
and check again for "sneaky" trace. Present now?

Referencing your post of 7/15/12 (below), it appears that adjustment may be
dependent on a calibration fixture which I don't (yet) have. Is there a way to
check/adjust that without that fixture?
That was about the "wavy" readout. All such adjustments are at the easy to reach
final amplifier boards and maybe Readout board. No extender or Signal
Standardizer calibration fixture needed.

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